1. Field of the Invention
The present invention relates to a semiconductor device that controls communication of data performed between a host device, such as a personal computer Personal Computer), and a peripheral device, such as a printer, a digital camera, and a digital audio player. Especially, the present invention relates to the semiconductor device for the technology performed using Universal Serial Bus (it is called USB hereinafter) with suitable data communications between the host device and the peripheral device. Furthermore, the present invention relates to a method for supplying a power supply voltage to such semiconductor device.
This application is counterpart of Japanese patent applications, Serial Number 299675/2000, filed Sep. 29, 2000, the subject matter of which is incorporated herein by reference.
2. Description of the Related Art
In recent years, a demand for a portable digital audio player etc. as a portable device has increased rapidly. Such portable device is mainly included a mounting board, a USB connector mounted on the mounting board, and a slot which can connect memories, such as a Flash memory. Further, a controller IC is mounted on this mounting board. The controller IC is made up of a USB control circuit (it is also called USB transceiver), a microcontroller unit (it is called MCU hereinafter), and an I/O block that performs the interface with an external device, such as Flash memory. These circuits are integrated into one chip as the controller IC. This mounting board is built in the digital audio player.
The USB connector can connect the USB and thus the PC as the host device and are connected to the portable device through the USB.
The USB control circuit has a function to receive data from the USB and a function which outputs data to the USB.
The MCU issues predetermined directions to the USB control circuit and the I/O block so that the these circuits can perform a predetermined operation.
Peripheral parts, i.e., memories such as Flash memory which stores music data etc., are connected to the slot.
The music data stored in the PC is transferred to the portable device through the USB under control of the PC, and transferred music data is stored in the Flash memory through the USB control circuit based on control of the MCU. Moreover, data stored in the Flash memory is transferred to the PC through the MCU, the USB control circuit, and the USB under control of the MCU, and transferred music data is stored in the PC. As described above, the USB is used to transfer contents data, such as music data, between the PC and the portable device.
Although the above portable devices are portable therefore, they are driven by a battery. Therefore, in order to reduce consumption of a battery, an operation voltage in the portable device must be set up low. Here, the operation voltage means that the power supply voltage supplied to the portable device.
However, since the operation voltage of the USB control circuit and the Flash memory is standardized, the operation voltage of the peripheral part cannot disregard this standardized operation voltage, and cannot set it low. That is, the minimum operation voltage of the peripheral part depends on the standardized operation voltage of the USB control circuit and the I/O block.
Therefore, the further lower power consumption of the whole peripheral device (whole digital audio player) cannot be expected. Especially, since the USB control circuit operates in response to a clock signal having relatively high frequency while data communications are performed using the USB, consuming battery power is hard. Consequently, the semiconductor device having improved power consumption has been desired.